[whpalmer4]

If you are changing the due date on an action contained in a project which also has a due date, the project's due date will be used for display purposes if it is earlier than the action's. It isn't necessarily obvious that this is taking place, because you'll see the date you set for the action if you look in the due date column or the due date field in the inspector, but for the purposes of sorting the view, grouping the view, or styling the actions, the more restrictive due date will be used.